This invention relates to the enzymatic hydrolysis of cellulosic materials, particularly cellulosic wastes.
Hydrolysis of cellulose yields a mixture of simple reducing sugars, mainly glucose. These hydrolysis products can be converted to ethyl alcohol which can be used as a liquid fuel to replace petroleum, or they can be converted to methane which can be a useful source of gaseous fuel. Or the hydrolysis products can be used to manufacture various organic chemicals presently produced from petroleum. In terms of available energy, expressed either as the heat of combustion of cellulose or of the glucose or alcohol theoretically obtainable therefrom, a pound of cellulose is equivalent to 0.35 lb of gasoline (7200 BTU).
On the land area of the earth about 1.6 .times. 10.sup.10 tons of carbon are fixed every year by photosynthesis, out of which about half appears in the form of cellulose. The sheer magnitude of this potential source dictates the necessity of improving the scientific and technological capabilities for cellulose utilization. In the North American continent certain cellulosic materials are available for economic processing at this time. Two hundred ninety million tons per year of residential, institutional and commercial solid wastes containing approximately fifty percent paper and other cellulosic materials are produced in the United States. In addition, about sixty million tons of bagasse are available. These altogether contain about one hundred and twenty million tons of cellulose, the energy equivalence of which is about a fifth of the current U.S. gasoline consumption. Furthermore, 2.3 billion tons per year of agricultural wastes in the United States, having a very high cellulose content, increase the supply significantly. In spite of these various sources of available cellulose, a major industrial alcohol fermentation process can only be successful if the reducing sugars are available at a sufficiently low price.
Most early efforts in this field were geared to the acid hydrolysis of wood products to sugars. The most notable process in this context was the Bergius process in the 1930's (Bergius, F., Ind. Eng. Chem., 29, 247, 1937). However, acid hydrolysis requires costly materials of construction because of the inherent problems of corrosion. In recent years, cellulose degradation through enzymatic means has been a subject of investigation by various workers.